The present invention relates to an ink-jet printer for printing an image on a print medium with ink ejected from a print head and particularly, to an ink-jet printer in which ink is supplied to a print head through a tube from an ink tank.
A serial ink-jet printer has heretofore prevailed. The serial ink-jet printer comprises a carriage movable along a guide bar extending across a paper sheet and a print head which is mounted on the carriage and driven as the carriage moves. The print head is mounted on the carriage along with an ink cassette of a relatively small capacity to eject ink supplied from the ink cassette toward the paper sheet. The paper sheet is fed in a direction perpendicular to the guide bar for each carriage movement. In the case where the print head and the ink cassette are moved by the carriage, the print speed is limited and there is a problem in that the capacity of the ink tank cannot be increased due to an influence on a load and inertia of the carriage. Hence, the ink-jet printer is not suitable for obtaining a great number of prints in a short period of time.
For example, Jpn. Pat. Appln. KOKAI Publication No. 10-138520 filed by the applicant of the present application discloses a rotary drum ink-jet printer which can obtain a great number of prints in a short period of time. The ink-jet printer comprises a rotary drum for rotating in one direction and a print head for printing an image on a paper sheet which is held on the rotary drum and moves together with the rotary drum. The print head has a plurality of ink-jet nozzles aligned in a axial direction of the rotary drum to eject ink toward the paper sheet. The ink is supplied via a tube from an ink tank which has a large capacity and is disposed in an open space remote from the print head. Since the rotary drum ink-jet printer does not require movement of the print head, printing can be performed at a speed higher than that of the serial ink-jet printer. In addition, a great number of prints can be obtained for each supplement of ink.
If the amount of remaining ink becomes small, ink is supplemented in both the serial or rotary drum ink-jet printer. Generally, an ink supplement request is issued in the ink-jet printer when the remaining ink reaches less than a reference amount which is slightly larger than that required for obtaining a predetermined number of prints, and printing is stopped when the predetermined number of prints has been obtained after issuance of the request.
However, after printing has been stopped in this way, the printer cannot perform a test printing of a single sheet for checking a layout of an image and its color arrangement, for example. Further, this ink-jet printer cancels a maintenance process after issuance of the ink supplement request, since the maintenance process consumes ink for a purpose other than printing. In the maintenance process, ink is spat to eliminate a disorder of a print head such as unstable ink ejection caused by increase in viscosity of ink or a change in ink characteristics. Thus, print quality may be degraded due to canceling of the maintenance process. If printing is continued without canceling the maintenance process, ink shortage arises during the printing. Such a maintenance process is disclosed, for example, in Jpn. Pat. Appln. KOKOKU Publication No. 3-59832 and Jpn. Pat. Appln. KOKAI Publication No. 3-5154.
The rotary drum ink-jet printer has an advantage that a great number of prints can be obtained within a short period of time. However, an average number of prints continuously obtained for each print job is remarkably varied with the environment in which the printer is used. Therefore, it is difficult to determine from such an average the number of prints to be obtained after issuance of the ink supplement request. In the environment where a print job of continuously obtaining about 50 A4-size prints is frequently ordered, if the predetermined number of prints is determined at a value less than 50, each print job is very likely to be interrupted due to a stop of printing. To the contrary, if the predetermined number of prints is determined at a value more than 50, an ink supplement request is issued earlier in a state where a large amount of ink remains. On the other hand, the printer must be arranged such that printing is stopped before air intrudes into the tube from the ink tank due to consumption of ink, since a significant amount of time and labor is required to remove air from the tube. In a case where the ink-jet printer is shared by a plurality of computers through a network, print jobs for obtaining a great number of prints are frequently ordered by the computers and stacked in the printer. Since the printer must determine the number of prints to be obtained after issuance of the ink supplement request and interruption timing of printing while performing a control for the print jobs, the determination becomes difficult and complicated.